1. Field of the Invention
Example embodiments generally relate to a fixing device and an image forming apparatus, and more particularly, to a fixing device for fixing a toner image on a recording medium and an image forming apparatus including the fixing device.
2. Description of the Related Art
Related-art image forming apparatuses, such as copiers, facsimile machines, printers, or multifunction printers having at least one of copying, printing, scanning, and facsimile functions, typically form an image on a recording medium according to image data. Thus, for example, a charger uniformly charges a surface of an image carrier; an optical writer emits a light beam onto the charged surface of the image carrier to form an electrostatic latent image on the image carrier according to the image data; a development device supplies toner to the electrostatic latent image formed on the image carrier to make the electrostatic latent image visible as a toner image; the toner image is directly transferred from the image carrier onto a recording medium or is indirectly transferred from the image carrier onto a recording medium via an intermediate transfer member; a cleaner then collects residual toner not transferred and remaining on the surface of the image carrier after the toner image is transferred from the image carrier onto the recording medium; finally, a fixing device applies heat and pressure to the recording medium bearing the toner image to fix the toner image on the recording medium, thus forming the image on the recording medium.
Such fixing device may include a fixing rotary body heated by a heater, and an opposed rotary body that presses against the fixing rotary body to form a fixing nip therebetween. As a recording medium bearing a toner image passes through the fixing nip, the fixing rotary body and the opposed rotary body apply heat and pressure to the recording medium to melt and fix the toner image on the recording medium. Thereafter, the recording medium bearing the fixed toner image is discharged from the fixing nip.
However, it can happen that the recording medium bearing the toner image facing the fixing rotary body gets stuck to the surface of the fixing rotary body due to the adhesive force of the melted toner of the toner image. As a result, the recording medium may not be discharged from the fixing nip properly.
To address this problem, a separator such as a blade or a wedge may contact the surface of the fixing rotary body against the direction of rotation of the fixing rotary body to separate the recording medium from the fixing rotary body. However, because the separator remains in constant contact with the fixing rotary body, the surface of the fixing rotary body contacted by the separator experiences wear over time. As a result, the worn fixing rotary body may generate streaks and uneven glosses on the toner image.
To address this problem, the fixing device may further include a separator protection mechanism disposed downstream from the fixing nip in the conveyance direction of the recording medium to separate the separator from the fixing rotary body. When the recording medium lifts the separator protection mechanism, the separator, which is interlocked with the separator protection mechanism via a connecting member, is separated from the fixing rotary body. Accordingly, whenever the recording medium passes through the fixing nip and lifts the separator protection mechanism, the separator is separated from the fixing rotary body, shortening the time period for which the separator contacts the fixing rotary body and therefore minimizing wear of the surface of the fixing rotary body due to friction caused by the separator sliding over the fixing rotary body.
However, a separator configured to separate from the fixing rotary body only when the recording medium passes through the fixing nip as described above may not be effective in reducing wear of the surface of the fixing rotary body during warm-up of the fixing device, because more time is used to warm up the fixing device or to idle the fixing rotary body than to feed the recording medium through the fixing nip.
Alternatively, the fixing device may include a sensor that detects the recording medium conveyed toward the fixing nip and a solenoid that controls the separator based on a detection signal sent from the sensor. With this configuration, the separator contacts the fixing rotary body only when the recording medium passes through the fixing nip. Accordingly, the separator remains isolated from the fixing rotary body otherwise and thus for a longer time compared to a configuration in which the separator separates from the fixing rotary body only when the recording medium passes through the fixing nip, thus decreasing wear of the fixing rotary body.
However, each separator requires its own solenoid. Consequently, when a plurality of separators is provided in the fixing device, a plurality of solenoids is needed, upsizing the fixing device and increasing manufacturing costs. Moreover, when each of the plurality of solenoids is designed to respond at different times, the plurality of separators may not move simultaneously.
To address this problem, the plurality of separators may be combined with each other and a single solenoid may move the combined separators collectively. FIG. 1 is a schematic view of a known fixing device 20R including a plurality of separators 230 connected to each other by a connecting member 220, and contacting a fixing rotary body 210 to separate the recording medium from the fixing rotary body 210.
However, if there are variations in the dimensions of the individual separators 230 or the fixing rotary body 210 is bent or vibrates, a slight gap S may arise between one of the plurality of separators 230 (for example, the center separator 230) and the fixing rotary body 210. As a result, if all of the separators 230 do not contact the fixing rotary body 210 simultaneously, the recording medium may not be separated from the fixing rotary body 210 properly.